An exhaust gas sampling mechanism has partially sampled exhaust gas flowing through a flow path such as an exhaust pipe, and the exhaust gas has been led into an exhaust gas analysis apparatus for analyzing exhaust gas components such as carbon monoxide (CO), carbon dioxide (CO2), nitrogen oxide (NOX), and total hydrocarbon (THC).
As FIG. 7 illustrates, the exhaust gas sampling mechanism 3A includes an attachment pipe 31A, a sampling probe 32A, and a protection pipe 34A (See U.S. Pat. No. 8,087,308). The attachment pipe 31A is attached to the open end of the exhaust pipe of a vehicle. The sampling probe 32A is inserted from the lateral surface of the attachment pipe 31A into the attachment pipe 31A. The protection pipe 34A has a substantially cylindrical shape, and covers the periphery of the sampling probe 32A in the flow path.
Only the downstream surface of the protection pipe 34A has an opening in a flow path through which exhaust gas flows. The exhaust gas enters the protection pipe 34A through the opening on the downstream side, and the entered exhaust gas is sampled by the sampling probe 32A. This configuration prevents solid components such as ash and dusts in the exhaust gas from entering the sampling probe 32A from the upstream surface of the protection pipe 34A, thereby preventing a malfunction such as clogging in the sampling probe 32A.
However, in the above configuration of the protection pipe 34A, when condensed water droplets in the exhaust gas come to the protection pipe 34A, the condensed water droplets may enter and be accumulated in the protection pipe 34A. When, for example, water W accumulated at the bottom of the inside of the protection pipe 34A evaporates, the concentration of water in the exhaust gas becomes abnormally higher than the normal concentration of water. This may adversely affect not only the measurement of the concentration of water but also the measurement accuracy of other exhaust gas components due to water interference and others. Moreover, as FIG. 6 illustrates, the protection pipe 34A has the opening into which the exhaust gas flows in the direction opposite the direction in which the whole exhaust gas flows. Therefore, it is difficult for the exhaust gas to enter the protection pipe 34A, which leads a decrease in response speed in analysis by an exhaust gas analysis apparatus.